Contemporary vehicle's often employ Remote Keyless Entry (R.K.E.) systems that include control functions such as those to unlock doors of the vehicle, start the engine in the vehicle, or to open a garage door. Typically radio signals are transmitted from an R.K.E. transmitter which is typically a portable device, to an R.K.E. receiver which is typically mounted in a vehicle or in a garage.
Once appropriate signals have been received, transducers associated with the R.K.E. receiver will activate and control various physical behaviors. For example, if a message is transmitted from the R.K.E. transmitter commanding to lock a door of the vehicle, the receiver decodes it and commands a lock transducer to lock the vehicle's door.
Often vehicles have built-in alarm systems that can be activated, for instance, when someone attempts to break into the vehicle. When the vehicle's owner returns to the vehicle, the owner will attempt to shut off the alarm using the R.K.E. transmitter. The problem with this approach is that the deactivation message transmitted from the R.K.E. transmitter can overlap with activation of the alarm--which is pulsed on and off periodically. While the alarm is sounding electrical disturbance it causes can cause the R.K.E. receiver to improperly decode the transmitted message. An example of such an operation is shown in FIG. 1.
A first waveform 101 indicates when the alarm is active. Commencing at reference number 105 the alarm is activated. At reference number 107 the alarm is deactivated. The period between reference numbers 105 and 107 may be on the order of one second. The alarm remains silent until reference number 113 where it is again reactivated until reference number 117.
A second waveform 103 indicates when messages are transmitted from the R.K.E. transmitter. A first message commences at reference number 109 and concludes at reference number 111. Note there is no overlap between the activated alarm and the first message. When this happens the first message is easily decoded without interference from the alarm. Next, a second message is transmitted from the R.K.E. transmitter between reference numbers 115 and 119. As mentioned earlier, at reference number 113 the alarm is activated. Because the activation of the alarm overlaps the transmission of the second message from the R.K.E. transmitter, the second message may not be correctly decoded. If the second message requested that the alarm be deactivated, then the alarm would not be shut off.
Summarizing, while the R.K.E. receiver can correctly detect the presence of the transmitted message the alarm causes the transmitted message data to be corrupted so that the alarm cannot be deactivated.
Since transmission of the message and activation of the alarm are time independent, adjustment of their respective periodic behavior will not be an acceptable solution.
What is needed is an improved approach that will enable proper decoding of a received message without interference by the alarm.